Shear isolated hydrophone

ABSTRACT

An acoustic sensor may include a base, a diaphragm, and a piezoelectric film. A cup may be disposed around the sensor. A filling material may be injected inside the cup and around the sensor. An end cap may be placed at an end of the cup to enclose the filling material within the cup. The cup may include longitudinal fibers disposed in an adhesive matrix. The acoustic sensor and the cup may be encapsulated in a molding material using a reaction injection molding (RIM) process to form a sensor section. Buoyant sections may be formed between sensor sections on a strain member. Buoyant sections may be formed by encapsulating a portion of the strain member in a buoyant molding material using a RIM process. be The strain member, the sensor sections, and the buoyant sections may be joined to form an array.

PRIORITY CLAIM

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 09/635,031 which was filed on Aug. 4, 2000. Theabove-referenced application is incorporated by reference as if fullyset forth herein.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to acoustical sensors. Anembodiment relates to an acoustic sensor that has high sensitivity, arobust response, and a substantially reduced response to longitudinal orshear forces present at a flow boundary of an acoustic sensor array.

[0004] 2. Description of Related Art

[0005] Acoustical sensors may be used to measure sound transmittedthrough water. One type of acoustical sensor is a hydrophone. A numberof hydrophones may be coupled together to form an acoustic sensor array.Acoustic sensor arrays may be used as detection instruments to monitorvessel movement in a marine environment. Acoustical sensor arrays may beused during seismic surveys of water covered areas to estimate thelocation of underground formations and structures. Acoustical sensorarrays may be placed in liquid filled wellbores. Such acoustical sensorarrays may be used to conduct vertical seismic surveys. Acousticalsensor arrays may be used as sensors for a variety of other applicationsas well.

[0006] One type of acoustic sensor array is a liquid filled array. Theacoustic sensor array, which may be over 8 kilometers in length, mayinclude a number of active cable sections. Each active cable section mayinclude several groups of hydrophones connected in series. Thehydrophones may be placed within a flexible, sealed tubular outer jacketthat is made of polyurethane or a similar material. Multiple strainmembers (generally between two and five) may be axially spaced apartalong the length of the array within the outer jacket. The strainmembers may be cables; such as, but not limited to, steel cables, Kevlarreinforced cables and/or Vectran cables. The strain members may bear theload of the array when the array is towed or otherwise supported. Thearray may be filled with a nonconductive, light fluid, such as kerosene,to provide the array with a desired buoyancy.

[0007] Liquid filled arrays may have several characteristics that areundesirable. The arrays may be difficult and labor intensive toconstruct. The arrays may have to be stored on reels that have largediameters (greater than 10 feet) to inhibit damage to the array. Thearrays may have inherent sensitivity limitations due to noise generatedwithin the array by the fluid during use. The arrays may need to betowed at depths from about 12 to 30 feet below water surface to minimizesurface reflection noise and surface wave noise. The arrays may presentsignificant safety, health and environmental problems should the outercasing leak or rupture.

[0008] A second type of acoustical sensor array is a solid or non-liquidfilled acoustic sensor array. U.S. Pat. Nos. 6,108,274; 6,108,267;5,982,708; 5,883,857; 5,774,423; 5,361,240; and 4,733,378, each of whichis incorporated by reference as if fully set forth herein, describenon-liquid filled arrays and hydrophones for non-liquid filled arrays.Non-liquid filled arrays may be easier to manufacture, may be used atshallower depths and may have hydrophone responses that are moresensitive and robust than the response obtainable from a liquid filledarray.

[0009] A hydrophone may produce electrical signals in response tovariation of acoustic wave pressure across the hydrophone. Severalhydrophones may be electrically coupled together to form an activesection of an acoustic sensor array. There may be several separateactive sections within an acoustic sensor array. Electrical signals frommultiple hydrophones of an active section may be combined to provide anaverage signal response and/or to increase the signal-to-noise ratiowithin an active section of the array. Hydrophones may be coupledtogether in serial and/or parallel arrangements so that active sectionsof the array have a desired response and sensitivity to acousticalwaves. Typically, fewer hydrophones are needed in an active section ofthe array if the individual hydrophones have a high signal-to-noiseratio. The use of hydrophones having high signal-to-noise ratios allowsfor shorter, sensitive and robust acoustic sensor arrays. Hydrophones ofnon-liquid filled arrays may have an increased signal-to-noise ratio ascompared to typical hydrophones of liquid filled arrays.

[0010] One type of non-liquid filled acoustic sensor array is a“floatation” cable design. The design includes a buoyant material, suchas foamed polyethylene, that is formed over an inner jacket. The buoyantmaterial is then covered with a polyurethane outer jacket. The types ofmaterial used for a floatation cable design may not allow the buoyantmaterial to bind to the outer jacket or the inner jacket. If the outercasing were to be ruptured during use, water that entered into the arraywould undesirably be able to migrate up and down the length of thecable.

SUMMARY OF THE INVENTION

[0011] An acoustic sensor array may include a strain member, sensorsections and buoyancy sections. The sensor sections and the buoyancysections may alternate along a length of the strain member. The sensorsections may be placed along a length of the strain member. Each sensorsection may include one or more sensors capable of detecting acousticsignals. The sensors may be electronic sensors or fiber optic sensors. Apotting material may be used to fill the space between a body of thesensor sections and the strain member. Buoyancy sections may be formedbetween adjacent sensor sections. The buoyancy sections may be formed ofmaterial that provides a desired amount of buoyancy for the array. Whenthe buoyant sections are formed, the material of the buoyant sectionsmay bind to the sensor sections. The material may also bind to thestrain member. Filling the space between the strain members and thebodies of the sensors with potting material, and binding the buoyantsections to the sensor sections makes the array substantially anintegral, solid unit. If one of the sections were to crack, migration offluid in the array would be inhibited beyond the extent of the crack. Inaddition, the material used to form outer portions of the array may bemade of a polymer material, such as polyurethane, that is resistant tocracking and/or breakage during use.

[0012] A sensor of a sensor section may be encapsulated within a polymerbody. In an embodiment, the polymer is a polyurethane. To form a sensorsection, positioners may hold a sensor at a desired position within amold. Wiring for the sensors may be spiral wound about one, or both, ofthe positioners. Spiral winding the wiring may inhibit strain damage tothe sensors due to bending of the array during use or during storage ona reel. The positioners may be made of, or coated with, a material thatdoes not bind to the polymer so that the positioners may be removedafter encapsulation of the sensor. The polymer is injected into the moldto form the sensor section. The mold may be part of a reaction injectionmolding machine. The polymer may be a material that is capable ofbinding to the material used to form buoyancy sections of a sensorarray. The sensor sections may be formed so that the ends of the sensorsections have large surface areas that will bind to ends of buoyancysections. A binding film may be wrapped on the ends of the sensorsections, and/or a binding fluid may be placed on the ends of the sensorsections, to enhance binding between the sensor sections and thebuoyancy sections.

[0013] A sensor of a sensor section may be a hydrophone. The hydrophonemay include a base that forms a back plane for a sensor. The base mayhave a number of ridges that form a plurality of concave surfaces in anouter surface of the base. In an embodiment, the base may have eightridges so that the back plane has a generally octagonal cross sectionalshape with eight concavely curved sides. Other back planes may havecross sectional shapes having fewer or more than 8 sides. A back planemay be molded or placed on the base, or the back plane may be anintegral part of the base. A flexible diaphragm may slide over the backplane. In an embodiment, the diaphragm may have a cross sectional shapethat substantially matches the cross sectional shape of the back planeyet allows air gaps to form between the concave sides and the diaphragm.In other embodiments, the diaphragm may have a different cross sectionalshape than the back plane. For example, in an embodiment, the back planehas a generally octagonal outer cross sectional shape with concavecurved sides and the diaphragm has a circular cross sectional shape. Asealant may be placed between the diaphragm and the back plane at bothends of the diaphragm. During use, the diaphragm is able to flex intothe concavities of the back plane in response to acoustical waves thatpass through the hydrophone.

[0014] A thin piezoelectric film may be wrapped around the diaphragm.The piezoelectric film may be made of polyvinylidiene fluoride. The filmmay include a conductive pattern. In an embodiment, the pattern isformed of a conductive ink. In other embodiments, the pattern may beformed by other techniques, such as etching. In certain embodiments, thepattern may include a number of conductive sections that are separatedby voids. The voids may be positioned above the ridges of the back planewhen the film is wrapped around the diaphragm and glued, taped, orotherwise sealed to the diaphragm during assembly. Small conductivetraces may connect conductive sections across the voids. When anacoustical wave passes through the sensor, the wave deflects thepiezoelectric film, and the film generates an electrical signal that istransmitted through the conductive pattern. Limited travel distancebetween the diaphragm and a concave surface of a back plane may inhibitstretching of the piezoelectric film beyond a yield limit of the film.Having only small conductive traces located at the ridges may reducepassive capacitance contributions from ridge supported portions of thepiezoelectric film. A dielectric film having an outer metallic coatingmay be placed around the piezoelectric film as an electromagneticshield.

[0015] The encapsulated sensors may be formed and individually testedfor operational performance before being joined together in anacoustical sensor array. A strain member may be threaded through apassage within each of the encapsulated sensors. The sensors may bespaced at desired positions along a length of the strain member. Wiringof the sensors may be spiral wound around the strain member. In anembodiment, the wiring is spiral wound around the strain member in thesame orientation as the winding within the encapsulated sensors. Activesections may be formed by coupling several sensors together in seriesand/or parallel configurations. Signal amplifiers may be coupled to thewiring where needed. The wiring of the sensors may be electricallycoupled to channels in or on the strain member. In an embodiment, thesensors of an active section are connected together and there is only asingle entry into a channel within the strain member regardless of thenumber of sensors that make up the active section. In an embodiment, thestrain member includes 24 separate channels. Each active section may betested to ensure that the active sections operate within desiredparameters. For each sensor, an end of the sensor may be plugged and thespace between the encapsulated sensor and the strain member may befilled with a potting material. The potting material may include fillermaterial, such as hollow glass beads. The filler material may helpestablish desired buoyancy within the sensor section. The pottingmaterial may be configured to bind to a coating of the strain memberand/or to the polymer material of the body of the sensor section.

[0016] Buoyancy sections may be formed between adjacent sensor sections.The sensor sections may be placed at each end of a mold. The mold may beclosed and polymer may be shot or produced within the mold to form abuoyancy section between the sensor sections. In an embodiment, the moldis part of a reaction injection molding machine. In an embodiment, themold produces buoyancy sections that have substantially the same outercircumference or perimeter that the sensor sections have. In otherembodiments, the mold produces buoyancy sections that have larger orsmaller outer circumferences or perimeters than the sensor sections. Thelarger or smaller outer circumferences may taper to the samecircumference or perimeter as the sensor sections. The material used toform the buoyancy sections, which may be a polyurethane, binds to theends of the sensors. A film or a coating may be placed on the ends ofthe sensor sections and/or the buoyancy sections to promote binding ofthe sensor sections to the buoyancy sections. The strain member mayinclude a coating, such as a polyurethane coating, that binds with thematerial of the buoyancy section when the buoyancy section is formed.

[0017] The material used to form the buoyancy sections may includefiller that allows the material to have a desired buoyancy. In anembodiment, the filler is hollow glass beads. The size of the hollowglass beads and the concentration of the glass beads may be adjusted sothat the array has a desired overall density. Buoyancy variations inbuoyancy sections of a sensor array may be desired along a length of thearray to counter the effect of sections of the array that are denserthan other sections. For example, ends of an array and sections thatinclude telemetry units may be denser than other sections of the array.The amount and/or size of hollow beads in the material used to form thebuoyancy sections adjacent to the ends and adjacent to telemetry unitsmay be adjusted to accommodate the greater density of these sections sothat the array has a desired overall buoyancy. The material used to formthe buoyancy sections may be adjusted so that the array will have asubstantially uniform buoyancy along a length of the array.

[0018] An advantage of a sensor array made of sensor sections, buoyancysections and a strain member is that the materials used to form thearray may have desirable properties and characteristics. For example,the primary material used to form an outermost layer of the array may bea polyurethane material that provides high resistance to physical damageto the array while still allowing the array to be flexible. The materialused to form the buoyancy sections may include filler material thatallows the buoyancy of the array to be controlled. The material used toencapsulate sensors within sensor sections of the array may not includefiller material if the filler material will decrease an energy ofacoustical waves passing through the material to the sensors.

[0019] An advantage of a sensor array made of sensor sections, buoyancysections and a strain member is that the array may have a small outerdiameter and a short length as compared to typical liquid filled arrays.Liquid filled arrays typically had to be wound on reels having diametersthat were greater than 10 feet. An array formed of buoyancy and sensorsections may have a small diameter and may be stored on reels havingsmall diameters. For example, an array may be formed that has an outerdiameter of about 1½ inches. Such an array may be stored on a reelhaving a diameter as small as about 1½ feet. Sensors within solid arraysmay be more sensitive than sensors within liquid filled arrays. Theincreased sensitivity may allow for more accurate detection of acousticsignals, and may allow for the use of arrays that are shorter than wouldbe practical if a liquid filled array were used. The use of shorterarrays having small outer diameters allows the arrays to be stored inless space and allows the arrays to be lighter and easier to manipulate.

[0020] An advantage of a sensor array made of sensor sections, buoyancysections and a strain member is that the sensor sections and thebuoyancy sections may bind together during formation of the array.Passages through the sensor sections may be filled with potting materialto seal the sensor sections to the strain member. Binding the sensorsections to the buoyancy sections and sealing the sensor sections to thestrain member may inhibit fluid migration within the array should thearray become cracked or damaged.

[0021] An advantage of a sensor array is that signals generated bysensors may be conveyed through electrical channels within a strainmember of the array. Several sensors may be electrically coupledtogether to form an active section of an array. In an embodiment, eachindividual sensor may be coupled to a channel within the strain member.In an alternate embodiment, a group of sensors may be electricallycoupled together and the group may be coupled to a channel of thesensor. Several groups may be coupled to one channel, or only one groupmay be coupled to one channel. Coupling only one group to a channel ofthe sensor array allows for a minimal number of entries into the strainmember to accommodate all of the sensors of the sensor array.

[0022] An advantage of a sensor array made of sensor sections, buoyancysections and a strain member is that controlling the material used toform the buoyancy sections may control the buoyancy of the array. Incertain embodiments the material used to form the buoyancy sections mayinclude filler. The filler may be a material, such as hollow glassbeads, having a selected size and concentration that will result in theformation of buoyancy sections having a desired buoyancy. The fillermaterial may be altered in various parts of the array to producebuoyancy sections that will accommodate different densities of the arrayat different locations along a length of the array. Space between thestrain member and the sensor sections may be filled with a pottingmaterial during formation to couple the sensor sections to the strainmember. The potting material may include filler material, such as hollowglass beads, to increase the buoyancy of the sensor sections of thearray. Further advantages may include that the sensor array is strong,sturdy, durable, lightweight, flexible, simple, efficient, safe,reliable and inexpensive; yet the sensor array may also be easy tomanufacture, handle and use.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Further advantages of the present invention may become apparentto those skilled in the art with the benefit of the followingdescription of the preferred embodiments and upon reference to theaccompanying drawings in which:

[0024]FIG. 1 depicts an embodiment of a sensor array;

[0025]FIG. 2 depicts a cross sectional view of a portion of a sensorarray, wherein a strain member of the array is not shown in section;

[0026]FIG. 3 depicts a representation of a reaction injection moldingsystem;

[0027]FIG. 4 depicts an end view of an embodiment of a diaphragmpositioned over an embodiment of a base;

[0028]FIG. 5 depicts a perspective view of an embodiment of a base for asensor;

[0029]FIG. 6 depicts a perspective view of an embodiment of a diaphragmfor a sensor;

[0030]FIG. 7 depicts a perspective view of an embodiment of a tubulardiaphragm;

[0031]FIG. 8 depicts a front view of an embodiment of a piezoelectricfilm;

[0032]FIG. 9 depicts a back view of the embodiment of a piezoelectricfilm depicted in FIG. 8;

[0033]FIG. 10 depicts a front view of an embodiment of a piezoelectricfilm;

[0034]FIG. 11 depicts an embodiment of a piezoelectric film having twopins;

[0035]FIG. 12 depicts a front view of an embodiment of a shield for asensor;

[0036]FIG. 13 depicts a cross sectional view of an embodiment of asleeve used during formation of a sensor section;

[0037]FIG. 14 depicts a perspective view of an embodiment of a mandrelused during formation of a sensor section having a single encapsulatedsensor;

[0038]FIG. 15 depicts embodiments of mandrels and sleeves coupled to anembodiment of a sensor;

[0039]FIG. 16 depicts a representation of an alternate process forassembling an array;

[0040]FIG. 17 depicts a cross sectional view of an embodiment of anarray using fiber optic sensors;

[0041]FIG. 18 illustrates a cross sectional view of an alternateembodiment of a sensor;

[0042]FIG. 19 illustrates a cross sectional view of more than one sensorsupported on a mandrel; and

[0043]FIG. 20 illustrates a cross sectional view of a molding machine.

[0044] While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and may herein be described in detail. Thedrawings may not be to scale. It should be understood, however, that thedrawings and detailed description thereto are not intended to limit theinvention to the particular form disclosed, but on the contrary, theintention is to cover all modifications, equivalents and alternativesfalling within the spirit and scope of the present invention as definedby the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

[0045]FIG. 1 depicts a representation of a sensor array 20. The array 20may be used for various purposes including, but not limited to,geological surveying of formations beneath a body of water, detectionand surveillance of acoustical sources in a marine environment, andgeological surveying of formations adjacent to an array positionedwithin a wellbore filled with fluid.

[0046] An array 20 may include ends 22, strain member 24 (shown in FIG.2), sensor sections 26, and buoyancy sections 28. Ends 22 of the array20 may be metallic connectors such as, but not limited to rings,threading, or quick releases. Typically, ends 22 are coupled to thestrain member and to buoyancy sections 28; though an end, or the ends,may be coupled to sensor sections 26, if desired. The types of ends 22at each end of an array 20 may be different. The ends 22 may allow thearray 20 to be maneuvered, handled, and coupled to an external supportand/or instrumentation. At least one end of the array 20 may include aconnector that allows the array to be coupled to a device that recordsand/or processes signals from the array. The connector may be anelectrical and/or fiber optic connector.

[0047] Buoyancy sections 28 and outer bodies of sensor sections 26 maybe formed by molding processes. In embodiments, bodies of sensorsections 26 and buoyancy sections 28 are formed by reaction injectionmolding (RIM) processes. Buoyancy sections 28 and sensor sections 26 mayhave hollow microspheres 27 (shown in FIG. 2). Other processes may alsobe used to form sensor sections and buoyancy sections. Such processesmay include, but are not limited to, injection molding and use ofthermosetting materials. RIM processes may advantageously be moreeconomical and less labor intensive than other processes that may beused to form sensor sections and/or buoyancy sections.

[0048]FIG. 3 depicts a schematic of an embodiment of RIM system 30. Atypical RIM system may be a Sure Shot 150 obtained from Hi-TechEngineering (Grand Rapids, Mich.). A RIM system 30 may include firstfeed tank 32 and second feed tank 34. The first tank 32 may hold a firstcomponent that is used to form a polymer during the RIM process. Thefirst component may be a polyol. The first component may includealcohol-terminated polyethers and polyesters. Examples ofalcohol-terminated polyethers include polyethylene oxide andpolypropylene oxide. An example of an alcohol-terminated polyester ispoly-1,4-butylene adipate. In some embodiments, the first component mayinclude dialcohols. Examples of dialcohols include ethylene glycol,diethylene glycol, 1,4-butanediol, and 1,6-hexanediol. The first tank 32may include a mixer that stirs fluid within the tank.

[0049] In some embodiments of a first component, an additive may beadded to the first component. The additive may be a polymerizationinitiator, or the additive may control physical and/or chemicalproperties of a polymer formed by a RIM process. For example, hollowmicrospheres may be added to the first component. The hollowmicrospheres may be added to control the density and/or buoyancy of thematerial produced by the RIM process. Different concentrations and/orsizes of hollow microspheres may be incorporated into different sectionsof a sensor array. In an embodiment, hollow glass microspheres are addedto buoyancy sections of the array so that the entire array hassubstantially neutral buoyancy in fresh water. If an array is neutrallybuoyant in fresh water, the array will be positively buoyant in salinewater. Weight may be added to the array during use in saline water sothat the array has neutral buoyancy in the saline water. It issignificantly easier to add weight to an array to make it less buoyantthan it is to increase the buoyancy of an existing array. In otherembodiments, the concentration and/or size of the hollow microspheres inan array is controlled so that the array will be substantially neutrallybuoyant in a fluid other than fresh water.

[0050] Hollow microspheres added to a first component may be subjectedto high shear forces during mixing and injection into a mold. The hollowmicrospheres may have high strength properties that inhibit breakdown ofthe microspheres during a RIM process. The microspheres may be smallenough to have negligible acoustic energy dissipation effect on acousticwaves passing through a sensor array. This allows the use of hollowmicrospheres in material that forms sensor bodies of sensor sections ofthe array. The hollow microspheres may be made of glass or othermaterial. The hollow microspheres may have densities that may beadjusted for a desired buoyancy. For example, a density of hollowmicrospheres may be between about 0.1 g/cm³ and about 0.9 g/cm³. In someembodiments, the hollow microspheres may have a density of about 0.38g/cm³. In an embodiment, the hollow microspheres are S-38 Scotchlitefrom 3M (St. Paul, Minn.). The hollow microspheres may be high strengthmicrospheres. In some embodiments of sensor arrays, sensor bodies may beformed without microspheres.

[0051] A second feed tank 34 may hold a second component that is mixedwith a first component to form a polymer during a RIM process. Thesecond component may be isocyanate. The isocyanate may be, but is notlimited to, toluene diisocyanate (TDI), methylene-4,4′-diphenyldiisocyanate (MDI), and polymeric isocyanate (PMDI) or mixtures thereof.In some embodiments of a RIM process, additives may be added to thesecond component as a polymerization initiator or to control chemicaland/or physical properties of a polymer produced by the RIM process. Thesecond feed tank 34 may include a mixer that stirs fluid within thetank.

[0052] Circulation pumps 36 may direct fluids in first feed tank 32 andsecond feed tank 34 to metering pumps 38. When fluid is not directed tothe metering pumps 38, the circulation pumps 36 may circulate fluid inthe first feed tank 32 back to the first feed tank and fluid in thesecond feed tank 34 back to the second feed tank. The circulation pumps36 may be low pressure pumps.

[0053] An additive may be introduced into the first feed tank 32 or thesecond feed tank 34 through entry ports in the tanks. Certain additivesmay tend to float on a top surface of fluid within a tank. Pipingleading from a circulation pump 36 to a tank may discharge recirculatedfluid above the top surface of fluid in the tank. The recirculated fluidmay wet the additive and force the additive into the fluid in the tank.Alternately, the additive may be added to piping that enters or leavesthe tanks.

[0054] Metering pumps 38 may control amounts of first component andsecond component that are sent to mixer 40. After mixing, the combinedfluid is directed to mold 42 within molding machine 44. After the mold42 is filled, excess mixed fluid may be discharged from piping leadingfrom the mixer 40 to the mold. The combined fluid is a reactive mixturethat forms a polymer within the mold 42. The combined fluid may flowrelatively easily for a short period of time. If the first component isa polyol and the second component is an isocyanate, the combined fluidwill produce a polyurethane.

[0055] After combined fluid has resided in a mold 42 for a sufficienttime to allow the fluid to form into polymer (typically less than 3minutes), the mold may be opened so that the formed product can beremoved from the mold. A molding machine 44 may be used to form sensorsections by encapsulating sensors within sensor bodies. The mold machine44 may form one or more sensor sections in one RIM cycle. The sensorsections may be tested, placed on a strain member, fixed at a desiredlocation on the strain member and electrically coupled together to formactive sections of an array. The molding machine 44 may subsequently beused to form buoyancy sections of a sensor array.

[0056] Buoyancy sections of an array may be formed using a moldingmachine 44. A mold 42 and the molding machine 44 may be the same moldand molding machine used to form sensor sections. Sensor sections andportions of strain member between the sensor sections may be placed inthe mold 42 of the mold machine 44. If a first or last section of anarray is to be formed, an end connector may be positioned at an end ofthe mold. The RIM system 30 may be cycled to form a buoyancy sectionover a portion of the strain member and between adjacent sensorsections, or between an end connector and a sensor section. The samematerial used to form the sensor sections may be used to form thebuoyancy sections. The material used to form the buoyancy sections mayinclude a buoyancy additive or filler, such as hollow microspheres. Oneor more buoyancy sections may be formed in one cycle of the RIM system.The mold may be opened, the formed section of cable may be removed fromthe mold, the strain member may be advanced to place sensor sectionswithout buoyancy sections in the mold, and the process may be repeateduntil all buoyancy sections of the array are formed. End connectors maybe molded to buoyancy sections at each end of an array.

[0057] Buoyancy variations in buoyancy sections of a sensor array may bedesired along a length of the array to counter the effect of sections ofthe array that are denser than other sections. For example, ends of anarray and sections that include telemetry units may be denser than othersections of the array. The amount and/or size of hollow beads in thematerial used to form the buoyancy sections adjacent to the ends andadjacent to telemetry units may be adjusted to accommodate the greaterdensity of these sections so that the array has a desired overallbuoyancy.

[0058] In some embodiments of sensor arrays, an outer surface shape ofsensor sections is different than the shape of the outer surface ofbuoyancy sections. Different outer surface shapes of sensor sections andbuoyancy sections may require the use of different molds to form thesensor sections and buoyancy sections.

[0059]FIG. 20 illustrates a cross sectional view of a molding machine44. A mold 42 for forming sensor sections and/or buoyancy sections maybe a two piece mold. First mold piece 46 may be attached to a firstportion of a molding machine 44, and second mold piece 48 may beattached to a second portion of the molding machine. The molding machine44 may be closed so that the first mold piece 46 and the second moldpiece 48 form a mold chamber. When a sensor section or buoyancy sectionis formed, mandrels or other positioners placed within the mold chambermay properly position or define features of the product being producedin the mold.

[0060] A first mold piece 46 may include a base with a half cylinderindentation running along a length of the base. A second mold piece 48may include a base with a half cylinder indentation that mates to thehalf cylinder of the first mold piece 46. The second mold piece 48 mayinclude fluid injection guides that distribute fluid evenly into a mold42 formed by the first mold piece 46 and the second mold piece. Thesecond mold piece 48 may also include vents 52 that allow air to bedisplaced from the mold as fluid is injected into the mold. The mold 42may include heater elements that heat surfaces of the mold totemperatures that inhibit fluid from a mixer 40 from condensing onsurfaces of the mold as fluid is injected into the mold. Mold releasecompound may be placed on the surfaces of the mold 42 so that a formedproduct may be removed from the mold when the mold is opened.

[0061] A molding machine 44 may rotate a closed mold approximately 90°prior to mold material being injected into the mold 42. In an initialposition, an interface 50 between a first mold piece 46 and second moldpiece 48 may be substantially parallel to the ground. This orientationfacilitates positioning of items within the mold 42 when the mold isopen. After the mold 42 is closed, the mold may be rotated about 90°about a center of the mold chamber so that the interface 50 is orientedsubstantially perpendicular to the ground. Mold material may be injectedinto the mold chamber so that material flows in an upward direction. Theperpendicular orientation of the interface 50 aligns fluid guides andvents of the mold in a vertical orientation that may promote uniformflow of material into the mold chamber.

[0062] A diameter of a cylinder formed by half cylindrical indentationsof a first mold piece 46 and a second mold piece 48 will typically bethe outer diameter of a product formed by the mold 42. Molds may beformed that produce bodies with shapes other than cylindrical shapes.For example, molds may be formed that produce bodies having hexagonal,octagonal, or other cross sections. Molds may be produced that producebodies having diameters that vary along a length of the product. Forexample, a mold may produce a product that has a largest diameter at acenter of the product, and the diameter may taper towards each end ofthe product.

[0063]FIG. 2 depicts a cross sectional view of a portion of a sensorarray 20. Strain member 24 of the sensor array 20 may provide strengthto the array. The strain member 24 may be a multi-layer strength memberhaving high tensile strength and minimal diameter and weight. In certainembodiments, the strain member 24 may include a number of discretewiring channels for transmission of signals from sensors within thearray to internal or external instrumentation. In other embodiments,wiring for the sensors may be carried in a separate cable. The strainmember 24 may be, but is not limited to, steel cable, Kevlar cable,Zylon cable, or Vectran cable. Strain members 24 may be supplied from anumber of manufacturers, such as the Cortland Cable Company (Cortland,N.Y.). An outer surface of the strain member may adhere or bond topotting material 52 used to fill space between sensor sections 26 andthe strain member. The outer jacket of the strain member 24 may alsobind to the material used to form buoyancy sections 28. Typically, asensor array 20 may be formed with a single strain member 24, but insome embodiments, two or more strain members may be utilized in anarray.

[0064] A sensor section 26 of a sensor array 20 may include sensor 54,and body 56. The sensor 54 within a sensor section 26 may be any type ofsensor or instrument needed at a particular location within the sensorarray 20. For example, the sensor 54 may be a hydrophone. In anembodiment, the hydrophone may include a piezoelectric element thatgenerates an electrical response when subjected to deformation by anacoustical signal. Several sensors may be electrically coupled togetherto form an active section of the array. In an alternate embodiment, thehydrophone may be a digital sensor formed from a fiber optic cable. Thesensor sections 26 may also include other types of sensors andinstruments such as, but not limited to, amplifiers, telemetry modules,depth indicators, accelerometers, geophones, or other sensors. In somesensor array embodiments, a depth indicator is formed as a portion of anend connector of the array 20.

[0065] A sensor 54 of a sensor section 26 may be a hydrophone. FIG. 4depicts an end view of an embodiment of a hydrophone. The hydrophone mayinclude base 58, diaphragm 60, piezoelectric film 62 and wiring 64. FIG.5 depicts an embodiment of a base 58. The base 58 may include one ormore concave or recessed surfaces 66 defined by ridges 68. In anembodiment, there are eight (8) concave surfaces 66. In alternateembodiments, a base 58 may have fewer or more concave surfaces 66. Amaximum depth of the concave surfaces 66 may be sufficiently large toallow movement of the diaphragm and piezoelectric film of the sensorinto the concave surfaces when an acoustic signal deflects thediaphragm. The maximum depth may be sufficiently small to inhibitdeformation of the piezoelectric film beyond a yield limit of thepiezoelectric film when the diaphragm and piezoelectric film are fullydeformed within one or more of the concave surfaces 66. Inhibitingdeformation of the film beyond the yield point may inhibit damage tosensors of the sensor array due to large acoustic signals. Inhibitingthe deformation of the film beyond the yield point may allow the arrayto be submerged to any depth without the submersion depth causing damageto the sensors of the array.

[0066] A base 58 may be formed as a single piece by injection molding,or by reaction injection molding (RIM). A RIM system that producessensor sections and buoyancy sections may be used to produce bases whenan appropriate mold is placed within a molding machine of the RIMsystem. Alternately, the base 58 may include a plastic or metal firstportion with a raised portion formed or positioned on the base. Theraised portion may include one or more concave surfaces 66. The firstportion may have cylindrical or other geometry. The base 58 may includepassageway 70. A strain member may be positioned through the passageway70 during assembly of an acoustic sensor array.

[0067]FIG. 6 and FIG. 7 depict sensor diaphragm embodiments. A diaphragm60 of a sensor may slide over a base of the sensor. The diaphragm 60 maybe made of a flexible material. Portions of an inner surface of thediaphragm 60 may reside on ridges of a base. In the embodiment depictedin FIG. 6, the diaphragm 60 has substantially the same cross sectionalshape as a raised outer surface of the base, although curvature ofconcave surfaces of the diaphragm are different than curvature ofconcave surfaces of the base to allow formation of air gaps 72 (depictedin FIG. 4) between the diaphragm and base. FIG. 4 depicts an end view ofa base 58 and diaphragm 60 wherein the diaphragm has substantially thesame cross sectional shape as the base. In an embodiment, the diaphragm60 may include an end surface that contacts an end surface of ridges ofthe base 58. Insertion of the diaphragm 60 over the base 58 may belimited by the diaphragm end surface contacting the base ridges endsurface. In an alternate embodiment, a diaphragm does not include an endsurface. When the diaphragm 60 is positioned over the base 58, a sealantmay seal the diaphragm to the base at each end of the diaphragm toinhibit axial movement of diaphragm relative to the base. Sealant atboth ends of the diaphragm 60 may inhibit escape of air from air gaps 72between the base 58 and the diaphragm during use.

[0068] In other diaphragm embodiments, the diaphragm may have adifferent cross sectional shape than a cross sectional shape of a baseover which the diaphragm is to be placed. For example, the tubulardiaphragm 60 depicted in FIG. 7 may slide over the octagonal base 58depicted in FIG. 5. A sealant may be positioned at each end of thediaphragm to inhibit axial movement of diaphragm relative to the base.Sealant at both ends of the diaphragm may inhibit escape of air from airgaps 72 between the base 58 and the diaphragm 60.

[0069] As depicted in FIG. 4, a sensor 54 may have air gap 72 formedbetween an outer surface of a diaphragm 60 and a concave surface 66 of abase 58. When an acoustical signal passes through the sensor 54, theacoustic signal may deflect the diaphragm 60 into the gap 72. Apiezoelectric film 62 that is wrapped around the diaphragm 60 may alsobe deflected into the gap 72. The piezoelectric film 62 may generate anelectrical signal that is proportionate to the amount of deformationthat the film is subjected to.

[0070] Piezoelectric film 62 may be wrapped around a diaphragm 60 of asensor 54. The piezoelectric film 62 may be glued, taped, or otherwisefastened to the diaphragm 60 to inhibit the film from separating fromthe diaphragm. One adhesive that may be used to couple the film to thediaphragm is 3M-VHB. The film 62 may wrap one or more times around thediaphragm 60. In an embodiment, an adhesive may be placed on the back ofthe film and a peel-off covering may be placed over the adhesive. Theadhesive and the covering may always be placed on a side of the filmthat will be biased with the same type of charge (positive or negative)when the film is deformed. Having the adhesive placed on the same sideof a film allows each film of an array to be oriented so that all filmsurfaces of an array that face diaphragms will generate the same type ofcharge (either positive or negative) when the film is deformed. Thecovering may be removed as the film is wrapped around the diaphragm. Apress or other instrument may be used to wind the film around thediaphragm to inhibit formation of gaps between layers of the film and toensure that the film is pressed against an outer surface of thediaphragm. The piezoelectric film 62 may be a polyvinylidiene (PVDF)film. In alternate embodiments, other piezoelectric materials may beused in lieu of a PVDF film. Wrapping the film 62 more than one timearound the diaphragm 60 may allow an acoustic signal that passes throughthe sensor 54 to deflect a large portion of the film. This may result inthe generation of a clear, strong signal in response to the acousticwave.

[0071]FIG. 8 and FIG. 9 depict front and back views of an embodiment ofa piezoelectric film 62 that may be used in a sensor. Piezoelectric film62 may have connector pins 74, and a conductive pattern on both faces ofthe film. The conductive pattern may be formed of a conductive metallayer deposited on the film. The metal may be, but is not limited to,gold, silver, copper, or aluminum. A conductive ink deposited on thefilm may be used to form the conductive pattern. The connector pins 74allow wiring 64 to be attached to the piezoelectric film 62. The wiring64 may be a twisted pair of electrical conductors. The wiring 64 mayinclude a ground conductor. The twisted pair of conductors of the wiring64 may be soldered to the pins 74 of the piezoelectric film 62.

[0072] A conductive pattern of a piezoelectric film 62 may include anumber of conductive areas 76, a number of nonconductive strips 78, anda number of small conductive strips 80 that electrically connect thelarge conductive strips together. A desired pattern may be deposited onthe piezoelectric film, or the pattern may be etched into a solidconductive layer placed on the film. The piezoelectric film 62 may bewrapped around a diaphragm and base of a sensor so that thenonconductive strips 78 are positioned above ridges of the base, and sothat the conductive areas 76 are positioned above concave surfaces ofthe base. When the piezoelectric film 62 is deflected by an acousticsignal, the deflection of the film causes the generation of a positivecharge at first film surface 82 and a negative charge at a second filmsurface 84. The charge generated by deflection of the film 62 may causean electrical signal to flow through the conductive strips 76 and thesmall conductive strips 80 to the wiring 64. Placing the nonconductivestrips 78 over the ridges of the base may reduce passive capacitancecontributions from ridge supported areas of the piezoelectric film 62that are not deformed by incident vibration.

[0073]FIG. 10 depicts a front view of an alternate embodiment of apiezoelectric film 62 having a large conductive area 76 withoutnonconductive areas separating portions of conductive area. The backsurface of the piezoelectric film 62 may also include a large conductivearea without nonconductive areas separating portions of conductive area.

[0074] Pins 74 may be coupled to conductive areas of a piezoelectricfilm 62. A first side 82 of the piezoelectric film 62 may haveconductive material adjacent to a pin 74, while an opposite surface doesnot include conductive material. Portions of the pin 74 may be pushedthrough the film 62 and bent over so that the pin is held to the film,and such that the pin is electrically coupled to the first side 82 ofthe film. A similar arrangement and connection may be made toelectrically couple a different pin 74 to an opposite side of the film62. In an embodiment of a piezoelectric film 62 illustrated in FIG. 8and in FIG. 9, a pair of pins 74 extend from opposite sides of the film.The pins 74 allow wiring 64 to be electrically coupled across thepiezoelectric film 62 to facilitate electrically coupling severalsensors together. In an alternate embodiment of a piezoelectric film 62illustrated in FIG. 11, the film may only have a pair of pins 74extending from one side of the film. Jumper wires that pass across thefilm, or wiring that is placed through a passage in a base of thesensor, may facilitate coupling several such sensors together.

[0075]FIG. 12 depicts an embodiment of an optional shield 86 for asensor. The shield 86 may be substantially the same size and shape as apiezoelectric film for the sensor. Pins 74 of the shield 86 may becoupled to a ground conductor of wiring for a sensor. The groundconductor may be coupled to a ground potential to minimize influence ofexternal voltage sources on the response of sensors of an array. Theshield 86 may include a substantially nonconductive base material, suchas a polyester, with a metal layer deposited on top of the base. In anembodiment, the base material is Mylar, though other types of materialmay also be used. The metal may be any type of conductor, such as, butnot limited to, gold, silver, copper, or aluminum. The embodiment of asensor shown in FIG. 4 includes a shield 86 over piezoelectric film 62.

[0076] Several piezoelectric films of an array may be electricallycoupled together in parallel and/or series configurations to createactive sections of the array. An active section may be spliced to anelectrical channel of the array. The electrical channel may be wiring ina strain member cable, or the electrical channel may be a channel of aseparate signal carrier. A strain member cable may have many channels.For example, a cable may have 12 channels. Cables having fewer or morechannels may also be used. The channels of an array may be coupled to anexternal recording device and/or data processor when the array is inuse. During production of the array, a splice into a channel may be madefor each sensor. In an alternate embodiment, several sensors areelectrically coupled together, and a splice into a channel is made forthe coupled together sensors. In an embodiment, all sensors of an activesection are coupled together and one splice into a channel is made foreach active section. This type of arrangement may minimize the number ofsplices required to form the array. Signal amplifiers may be coupled tothe sensors at selected locations in an array. The signal amplifiers maybe placed in sensor sections and/or buoyancy sections of the array.

[0077]FIG. 18 illustrates a cross sectional view of an alternateembodiment of a sensor 54. Base 58, diaphragm 60, and piezoelectric film62 may be configured as described in any of the embodiments herein. Cup450 may be disposed around the sensor 54. A first end of the cup 450 mayhave a surface with an inner diameter substantially similar to an outerdiameter of the first portion of base 58 so that the first end of thecup substantially encloses the diaphragm 60 and the raised portion ofthe base. A sealant may seal the cup 450 to the base 58 to fix aposition of the cup on the base. Cup 450 may have an inner diameterlarger than a maximum diameter of the diaphragm such that a relativelysmall air space is formed between the cup and the diaphragm. A fillingmaterial 456 may be injected through a second end of the cup 450 andinto the air space between the cup and the diaphragm. The fillingmaterial may be any fluid that may possess substantially similarproperties to a fluid. For example, the filling material may includeshore A-00 polyurethane. An end cap 458 may be placed at the second endof the cup 450 to enclose the filling material in the cup. A sealant mayseal the end cap to the cup. Use of the fluid-like filling material mayreduce coupling between the sensor and shear energies present at a flowboundary on an external surface of a sensor body or array. This maysubstantially reduce noise in the sensor and increase a sensitivity ofthe sensor.

[0078] Cup 450 may include longitudinal fibers disposed in an adhesivematrix. The longitudinal fibers may be carbon fibers. The adhesivematrix may include epoxy or any other suitable adhesive resin that maybond to the longitudinal fibers. Cup 450 may be formed by any methodthat may bond the longitudinal fibers into the adhesive matrix. Forexample, cup may be formed by a hand lay-up method. The hand lay-upmethod may include placing a hand of woven sheets of fiber upon a malemandrel. The adhesive material may be introduced to the woven sheets offiber at a high temperature and high pressure and allowed to cure. Insome embodiments, filament winding may be used to form cup 450. Infilament winding, fiber may be machine wound helically around a mandrel.The adhesive material may then be introduced to the fibers and thematrix cured at high temperature and pressure. Longitudinal fibers thatmay have good longitudinal strength but may have relatively little axialstrength may be formed using a pulltrusion method. Fiber filaments maybe fed into an extruding machine die and drawn through. This may resultin the fibers being embedded into a matrix in a substantiallylongitudinal direction. The matrix can then be cured at a relativelyhigh temperature and pressure. A cup formed by the pulltrusion methodmay be deformed in the axial direction in response to acoustic wavepressures. The longitudinal strength of the cup may inhibit deformationof the cup in the longitudinal, or non-axial, direction. This maysubstantially decouple the sensor from rendering a response tolongitudinal or shear forces imparted to the sensor or array.

[0079] A sensor 54 may be encapsulated within a body 56. FIG. 2 shows asensor 54 encapsulated within a body 56. The body 56 may be formed byinjection molding, reaction injection molding, or any other suitableprocess. The body 56 may include a passage through the body defined bysurface 88, and ends 90. A strain member 24 and/or wiring may bepositioned through the passage during production of a sensor array 20.The sensor 54 may be positioned at a desired location along a length ofthe strain member 24. Space between the surface 88 and the strain memberand/or wiring may be substantially filled with potting material 52 toseal the passage and to fix the location of the sensor section. Ends 90of the body 56 may have large surface areas. Large end surface areas mayprovide a large binding surface for joining sensor sections to buoyancysections 28.

[0080]FIG. 13 depicts a cross sectional view of an embodiment of asleeve 92 that may be used to form ends of a body of a sensor sectionduring encapsulation of a sensor. Inside surface 94 of the sleeve 92 maydefine an end surface of a sensor body. The sleeve may include anextension 96. The extension 96 may loosely mate to a recessed surface ofa mandrel. The loose mating may allow folia to be inserted against theinside surface 94 of the sleeve 92. The folia may promote formation of abond between an end surface of a sensor section and a buoyancy sectionwhen a buoyancy section is formed on the sensor section. The folia maybe a thin sheet of polymeric material, such as, but not limited to,polyurethane, polyester, or a combination thereof. For example, thefolia may be a low temperature polyurethane/polyester blend by DeerfieldPlastics Co. (South Deerfield, Mass.).

[0081]FIG. 14 depicts a perspective view of an embodiment of mandrel 98that may be used with a sleeve, such as sleeve 92 depicted in FIG. 13.The mandrel 98 may include base 100, shaft 102, groove 104, and wirepassage 106. A passage through the base 100 and shaft 102 may be formedto reduce the weight of the mandrel 98.

[0082] A base 100 of a mandrel 98 may be sized to fit within a channelin a mold of a molding machine. An outer surface of the base 100 mayhave the same circumferential (or perimeter) dimensions and shape as anouter surface of the sensor body to be formed. A surface of a sensorbody that defines a longitudinal passage through the sensor body may bedefined by a mandrel shaft 102 during molding of the sensor body. Oneend of the mandrel shaft 102 may be coupled to a base of a sensor. Asleeve, with a folia covered inner surface may be placed on the mandrel98 so that an extension of the sleeve fits within groove 104 in themandrel base 100. A base of a sensor may be positioned on an end of themandrel shaft 102. The end of the shaft 102 may include indentations 110that hold O-rings. O-rings positioned on the shaft 102 may contact thesensor base and inhibit injection of sensor body material into the basewhen the sensor body is formed. A small O-ring may be placed on thewiring of the sensor. The wiring may be wrapped around the shaft 102 ofthe mandrel 98. The wiring may exit the mandrel 98 through wiringpassage 106. The O-ring on the wiring may reside in an O-ring recess inthe wiring passage. The O-ring on the wiring may inhibit expulsion ofsensor body material from the mold adjacent to the wiring when thesensor body is formed.

[0083]FIG. 15 depicts coupled together sensor 54, mandrels 98 andsleeves 92 prior to insertion of the combination in a mold for formationof a sensor body around the sensor. Portions of the mandrel base 100 andshaft 102 that will be exposed to sensor body material during formationof the sensor body may be coated with a mold release compound prior tothe sleeves 92 and the sensor 54 being coupled to the mandrel 98. Folia112 may be positioned against an inside surface of the sleeve 92 andfolded over an outside surface of the sleeve before the sleeve ispositioned on the mandrel 98. In some embodiments, folia may not beused. In such embodiments, an inside surface of the sleeve may be coatedwith a mold release compound. O-rings may be placed on indentations inthe mandrel shaft. O-rings may also be placed on wiring 64 of the sensor54. The O-rings on the wiring 64 may pass through wiring passages in themandrels and the O-rings may be placed in O-ring recesses of themandrels.

[0084] Joined together mandrels, sleeves and sensors may be placed in amold to form a sensor section. The mold may be designed to form a singlesensor section, or the mold may form multiple sensor bodies. A moldrelease compound may be placed on portions of the mold that will contacta sensor body or excess portions of folia when the sensor body isformed. In an embodiment, the mold is part of a RIM machine. After thesensor body is formed, excess portions of folia may be trimmed from thesensor body. Excess sensor body material may also be trimmed from thesensor body.

[0085] In an embodiment, more than one sensor may be encapsulated in asensor section. A mandrel may be modified such that more than one sensormay be supported by the mandrel. FIG. 19 illustrates a cross sectionalview of an embodiment of more than one sensor supported on a mandrel 98.The mandrel may have a first piece 500 and a second piece 502. Firstpiece 500 and second piece 502 may be separated at junction 501 so thata first sensor 504 may be disposed on first piece 500. A second sensor506 may also be disposed on first piece 500. First piece 500 and secondpiece 502 may be recoupled at junction 501 and second sensor placedproximate junction 501 as shown in FIG. 19. At junction 501, first piece500 may have one end of reduced diameter so that the end may relativelysecurely be placed in a similarly reduced diameter opening in an end ofsecond piece 502. O-rings 508 may be disposed around the reduceddiameter end of first piece 500.

[0086] O-rings 510 may secure a position of first sensor 504 and secondsensor 506 on the first and second pieces of the mandrel as shown inFIG. 19. O-rings 510 may also inhibit injection of molding material intoan interior of sensor 504 or sensor 506. Sleeves 92 may be placed on themandrel. The sleeves may be configured as described in the embodiment ofFIG. 13. Folia may be positioned against an inside surface of sleeves 92as described in above embodiments. Wiring from sensors 504 and 506 maybe wrapped around a shaft of the mandrel and may exit through wirepassages as depicted in FIG. 14.

[0087] Sensors 504 and 506, mandrel pieces 500 and 502, and sleeves 92may be placed in a mold. The mold may be configured as described in anyof the embodiments herein. In some embodiments, the mold may be part ofa RIM machine. Sensor 504 and sensor 506 may be encapsulated in a sensorbody to form a sensor section. Excess portions of folia and sensor bodymaterial may be trimmed from the sensor body. The mandrel may also bemodified so that three or more sensors may be encapsulated in one sensorsection.

[0088] After a sensor is encapsulated in a sensor body to form a sensorsection, the sensor may be tested in a test machine to ensure that thesensor section produces a desired response to acoustical energy. Thetest machine may include a housing that surrounds the sensor body, aspeaker that generates acoustic waves, and an oscilloscope that connectsto wiring of the sensor section. Sensor sections may also be tested witha similar testing machine after the sensor sections are wired togetherand coupled to a wiring channel of the array, but prior to fixing theposition of the sensor sections on a strain member. This check allowsthe entire array to be tested for wiring errors prior to fixing thesensor sections to the strain member with potting material and prior toformation of the buoyancy sections.

[0089] A sensor array embodiment may be formed using a number of longbenches that support the entire length of an unformed array. An unformedarray includes end connectors, sensor sections and the strain memberwithout buoyancy sections. The long benches may be adjacent to ormovable to a molding machine of a RIM system. An end of a strain membermay be placed through passages of sensor sections as, or after, thestrain member is placed on the long benches. A first end connector maybe coupled to a first end of the strain member. The sensor sections maybe placed at desired positions along a length of the strain member.Wiring of each sensor section may be wrapped around the strain memberand electrically coupled to other sensor sections, to amplifiers, and/orto a wiring channel of the strain member. The wiring may be wrappedaround the strain member in the same direction (clockwise orcounterclockwise) as the wiring is wound within the sensor body 56.Wrapping wiring around a strain member and within a sensor body mayprovide strain relief for the wiring that inhibits stresses fromdeveloping within the wiring that will break electrical connectionswithin the array when the array is bent. The array may bend when storedon a reel or during use.

[0090] A second end connector may be coupled to a second end of thestrain member. The sensors of the array may be tested to ensure that allsensors and active sections of the array are working properly. A speakerbox may be placed over a sensor. Noise generated by the speaker may bemeasured by instrumentation attached to an electrical connection at anend of the array. After testing, a plug may be placed at an end ofsensor body. Potting material may be injected into a space between thesensor body and the strain member to fix the position of the sensorsection and fill the space between the strain member and the sensorbody. The potting material may be polyurethane. The polyurethane mayinclude a buoyancy modifier or other filler, such as hollowmicrospheres. After the potting material has set, the plug may beremoved and used with other sensor sections during injection of pottingmaterial.

[0091] An end connector nearest to a RIM machine of a RIM system may beattached to a cable. The cable may pass through the molding machine to areel. The cable may be used to pull the strain member into the molduntil the end connector is located at a first end of the mold and asensor body plugs the mold at a second end of the mold. The position ofthe remaining length of unformed array may be adjusted on the longbenches as the first end of the unformed array is pulled into the mold.The mold may be closed, and the RIM system may be cycled to form abuoyancy section or sections. The mold may be opened and the cable maybe used to draw the strain member forward until the next portion ofunformed array is positioned at a first end of the mold. Excess moldmaterial may be trimmed from the newly formed section of the arrayremoved from the mold. When a sufficient length of array with buoyancysections is formed to allow the cable to be attached to the reel, thecable may be attached to the reel, and formed portions of the array maybe wound on the reel to advance and position unformed portions of thearray in the molding machine. Trimming excess portions of mold materialfrom formed portions of the array, advancing unformed portions of thearray into the mold, closing the mold, cycling the RIM system, andopening the mold may be repeated until all buoyancy sections of the moldare formed. When forming the last section of the array, the second endconnector may be positioned at the second end of the mold.

[0092] Buoyant sections 28 of an array 20 may be formed between adjacentsensor sections 26. Certain instruments and/or sensors (such as signalamplifiers) may be positioned within buoyant sections when the buoyantsections are formed. A portion of the buoyant sections 28 may be formedof a material that provides buoyancy for the array. The amount ofbuoyancy in a specific section may be varied to accommodate variationsin weight along a length of the array 20. For example, more buoyancy maybe provided adjacent to heavier sections where connectors and/ortelemetry modules are located. In certain embodiments, hollowmicrospheres, or hollow glass spheres, may be introduced into materialused to form portions of the buoyant sections. The concentration and/orsizes of spheres may be adjusted to control the overall buoyancy of thearray. In an embodiment of a sensor array that is to be towed by avessel, the array may have a substantially neutral buoyancy in the waterthrough which the array will be towed.

[0093] Buoyant sections and sensor sections of an array may be formed sothat cross sectional shapes of the buoyant sections and sensor sectionsare substantially the same. The cross sectional shape of the buoyantsections and the sensor sections may be circular, but other crosssectional shapes, such as, but not limited to, ovoid, elliptical,rectangular, hexagonal, or octagonal may also be used. The circumferenceor perimeter of the buoyant sections and the sensor sections may besubstantially identical so that the sensor array has substantially thesame outer dimension along a length of the array. In alternateembodiments, the buoyancy sections may have larger or smallercircumferences or perimeters than the sensor sections. In suchembodiments, portions of the buoyancy sections may taper to the size ofthe circumference or perimeter of the sensor sections so that theresmooth transitions are formed between the buoyancy sections and thesensor sections.

[0094]FIG. 16 depicts a representation of an alternate process forforming an array. A strain member may be disposed on a first reel 202. Alength of the strain member may be placed on bench 204. A first end ofthe strain member may be placed through passages of sensor bodies 206.The bench 204 may be of sufficient length to support a selected numberof sensor bodies. The selected number of sensor bodies may be a numberof sensor bodies needed to complete an array. The first end of thestrain member may be placed through passages of each sensor bodydisposed on bench 204 such that each sensor body may be disposed on thestrain member. A first end connector may be coupled to the first end ofthe strain member at electrical assembly area 208. Second reel 216 maybe used to draw the strain member towards the second reel (from right toleft as depicted by arrow 220 in FIG. 16) and through electricalassembly area 208, first RIM press 210, second RIM press 212, and trimarea 214 by coupling a cable to the first end connector of the strainmember. The second reel 216 may be electrically controlled. First reel202 may have an electronic brake to apply tension to the strain memberduring an injection process.

[0095] As the strain member is drawn towards the second reel 216, a gatelocated at an end of bench 204 proximate electrical assembly area 208,may be used to determine a position of a sensor section on the strainmember. The gate may be a mechanical gate that is opened to allow asensor body to be drawn, along with the strain member, into electricalassembly area 208, or closed to inhibit a sensor body from being drawninto the electrical assembly area. Electrical connections betweensensors, amplifiers, the strain member, and/or other electronic devicesmay be made in electrical assembly area 208. Electrical wiring betweensensor bodies may be wrapped around the strain member as the strainmember is drawn towards the second reel by rotating each sensor body inan appropriate direction (clockwise or counter-clockwise). As describedin previous embodiments, the wiring may be wound around the strainmember in the same direction as wiring within the sensor body.

[0096] A sensor body may be drawn through electrical assembly area 208and into first RIM press 210. At first RIM press 210, molding material,such as polyurethane, may be injected into a space between the sensorbody and the strain member. The molding material may or may not includehollow microspheres. This process may fix the position of the sensorsection on the strain member and fill the space between the sensor bodyand the strain member as described in above embodiments. The strainmember may be drawn further towards second reel 216 and a second sensorbody may be drawn into the first RIM press 210 and injected with moldingmaterial. Additional sensor bodies may be drawn into the first RIM press210 and each injected with molding material. When a location selectedfor termination of a sensor group is reached at electrical assembly area208, connection between the sensor group and the strain member may bemade at the electrical assembly area.

[0097] After a sufficient number of sensor sections have been molded atthe first RIM press 210, the sensor sections may be drawn into secondRIM press 212. At the second RIM press 212, more than one sensor sectionmay be disposed in the RIM press to form buoyant sections, as describedin any of the embodiments herein. The molded buoyant sections and sensorsections may be drawn into trim area 214 where excess molding may betrimmed from the sections. The sections may be trimmed by hand or withan automated trimming system. The trimmed and molded sections may bewound onto the second reel 216. The process may be repeated until theentire array and all sensor bodies have been molded. The second endconnector may be coupled to a second end of the strain member. Theentire array may be wound onto the second reel 216 and be transported toa quality control area for testing or to a user of the array. Thealternate process described in the embodiment of FIG. 16 may besignificantly more automated and require significantly less space thanother processes. This may reduce costs related to, for example, capitalinvestment, labor, climate control, and/or taxes.

[0098]FIG. 17 depicts a cross sectional view of an alternate embodimentof an array 300 using fiber optic sensors. Sensors 302 may be fiberoptic sensors. Examples of fiber optic sensors are described in U.S.Pat. No. 5,317,544 to Maas et al. and U.S. Pat. No. 5,475,216 to Danveret al., which are incorporated by reference as if fully set forthherein. Sensors 302 may be coupled to each other using fiber optic cable306. Fiber optic cable 306 may include both a sensing fiber and areference fiber. Fiber optic cable 306 may include continuous fibersthat couple the sensors 302 in series in the array 300. Up to about 2000sensors may be coupled on a single fiber optic cable. An advantage isthat no electrical connection is needed between sensors 302 and strainmember 304. This may allow for simpler, faster construction of thearray.

[0099] Sensors 302 may be encapsulated in a molding material to formsensor sections 308 using a RIM system as described in aboveembodiments. The sensors may be molded one after the other, in series,so that the fiber optic cable 306 coupling the sensors is not broken ordamaged during the formation of the sensor sections. A mandrel, asdescribed in the embodiment of FIG. 14, may be used to support thesensors during a molding process. However, a wire passage on the mandrelmay have to be modified so that the fiber optic cable may be moldedwithout having to disconnect the fiber optic cable or sensors. Thesensor sections may be tested to ensure that the fiber optic cable andsensors produce desired responses to acoustical waves.

[0100] To form a fiber optic array, an end of strain member 304 may beplaced through passages of sensors 302, or sensor sections 308, on along bench or series of benches, as described in above embodiments. Thestrain member may be drawn through the passages so that the fiber opticcable coupling the sensors is not broken or damaged. In an embodiment,strain member 304 is a polymeric stress member such as an aramide stressmember. Fiber optic cable 306 may be helically wound around strainmember 304. The fiber optic cable may be wound in a direction identicalto a winding of the fiber optic cable in the sensor 302 (clockwise orcounter-clockwise). Winding the fiber optic cable around the strainmember and in the direction of the winding in the sensor may allow forstrain relief of the fiber optic cable. This may inhibit the cable frombreaking during storage on a reel and/or use.

[0101] A position of sensors 302 on the strain member 304 may be fixedeither by injecting a potting material in a space between the sensor andthe strain member as described above or by injecting a molding materialin the space using a RIM press as described above. The strain member andsensors may be drawn into a RIM system to form buoyant sections, asdescribed in above embodiments. This may provide buoyancy and protectionfor a fiber optic array. End connections may be made to each end of thefiber optic cable as described in previous embodiments.

[0102] Further modifications and alternative embodiments of variousaspects of the invention may be apparent to those skilled in the art inview of this description. Accordingly, this description is to beconstrued as illustrative only and is for the purpose of teaching thoseskilled in the art the general manner of carrying out the invention. Itis to be understood that the forms of the invention shown and describedherein are to be taken as the presently preferred embodiments. Elementsand materials may be substituted for those illustrated and describedherein, parts and processes may be reversed, and certain features of theinvention may be utilized independently, all as would be apparent to oneskilled in the art after having the benefit of this description of theinvention. Changes may be made in the elements described herein withoutdeparting from the spirit and scope of the invention as described in thefollowing claims.

What is claimed is:
 1. An acoustic sensor array, comprising: a strainmember having a length; sensor sections positioned along the length ofthe member, wherein at least one sensor is disposed within each sensorsection; buoyant sections positioned between the sensor sections; andwherein the strain member, the sensor sections, and the buoyant sectionsare joined to form the array.
 2. The array of claim 1, wherein at leastthe one sensor comprises a hydrophone.
 3. The array of claim 1, whereinat least the one sensor comprises a molded base.
 4. The array of claim1, wherein at least the one sensor comprises a molded base having aconduit, and wherein the strain member passes through the conduit in themolded base.
 5. The array of claim 1, wherein at least the one sensorcomprises a molded base having a plurality of ridges along its length.6. The array of claim 1, wherein at least the one sensor compriseshaving one or more concave surfaces.
 7. The array of claim 1, wherein atleast the one sensor comprises a molded base and a diaphragm, andwherein the molded base is inserted into the diaphragm.
 8. The array ofclaim 7, wherein the diaphragm comprises one or more concave surfaces.9. The array of claim 7, wherein the diaphragm comprises a tubularmember.
 10. The array of claim 7, wherein at least one air gap is formedbetween the molded base and the diaphragm.
 11. The array of claim 7,wherein an acoustic signal deflects the diaphragm towards the moldedbase during use.
 12. The array of claim 7, wherein at least the onesensor comprises a piezoelectric film.
 13. The array of claim 12,wherein the piezoelectric film surrounds a portion of the diaphragm. 14.The array of claim 12, wherein the piezoelectric film is fastened to thediaphragm.
 15. The array of claim 12, wherein the piezoelectric filmcomprises polyvinylidiene.
 16. The array of claim 12, wherein thepiezoelectric film surrounds a portion of the diaphragm, and wherein anacoustic signal deflects the diaphragm and the piezoelectric filmtowards the molded base during use.
 17. The array of claim 16, whereinthe piezoelectric film generates an electrical signal when deflectedtowards the molded base during use, and wherein a magnitude of theelectrical signal is proportional to an amount of deformation of thepiezoelectric film.
 18. The array of claim 12, wherein the piezoelectricfilm comprises a conductive pattern on a surface of the film.
 19. Thearray of claim 18, wherein the conductive pattern comprises at least oneconductive area and at least one non-conductive strip, wherein at leastthe one conductive area is positioned above a concave surface of themolded base, and wherein at least the one non-conductive strip ispositioned above a ridge of the molded base.
 20. The array of claim 18,wherein the conductive pattern comprises at least one conductive area,and wherein at least the one conductive area couples to at least one pindisposed on an edge of the piezoelectric film.
 21. The array of claim20, further comprising coupling at least the one pin to at least onewire.
 22. The array of claim 18, wherein the conductive patterncomprises metal.
 23. The array of claim 1, further comprising disposingat least the one sensor within a shield.
 24. The array of claim 23,wherein the shield is grounded.
 25. The array of claim 23, wherein theshield comprises a metal layer disposed on the polyester base material.26. The array of claim 23, wherein at least the one sensor comprises apiezoelectric film, wherein the shield has a substantially similar sizeand shape as the piezoelectric film, and wherein the shield is wrappedaround the piezoelectric film.
 27. The array of claim 1, furthercomprising a cup disposed around at least the one sensor.
 28. The arrayof claim 27, wherein the cup comprises longitudinal fibers disposed inan adhesive matrix.
 29. The array of claim 28, wherein the cup isconfigured to inhibit deformation of at least the one sensor in adirection of the longitudinal fibers during use.
 30. The array of claim27, further comprising a filling material disposed between the cup andat least the one sensor.
 31. The array of claim 30, wherein the fillingmaterial comprises A-00 polyurethane.
 32. The array of claim 30, whereinthe filling material is sealed within the cup.
 33. The array of claim30, wherein the filling material is configured to reduce couplingbetween at least the one sensor and shear energies present at a flowboundary on the array during use.
 34. The array of claim 1, wherein atleast the one sensor comprises a fiber optic sensor.
 35. The array ofclaim 1, further comprising a potting material disposed between eachsensor section and the strain member.
 36. The array of claim 35, whereinthe potting material substantially bonds to each sensor section and thestrain member.
 37. The array of claim 1, wherein the strain member, thesensor sections, and the buoyant sections are molded to form the array.38. The array of claim 1, wherein the sensor sections comprise areaction injection molded material.
 39. The array of claim 1, whereinthe sensor sections comprise hollow microspheres.
 40. The array of claim1, wherein the sensor sections comprise a polyurethane material.
 41. Thearray of claim 1, wherein the buoyant sections comprise a reactioninjection molded material.
 42. The array of claim 1, wherein the buoyantsections comprise hollow microspheres.
 43. The array of claim 1, whereinthe buoyant sections comprise a polyurethane material.
 44. The array ofclaim 1, wherein each buoyant section is substantially bonded to atleast one sensor section and the strain member such that fluid isinhibited from entering the array during use.
 45. The array of claim 1,wherein the buoyant sections have an outer diameter substantiallysimilar to an outer diameter of the sensor sections.
 46. The array ofclaim 1, wherein the array has a substantially constant outer diameter.47. The array of claim 1, further comprising an amplifier disposed in atleast one sensor section.
 48. The array of claim 1, further comprisingan amplifier disposed in at least one buoyant section.
 49. The array ofclaim 1, further comprising a telemetry module disposed in at least onebuoyant section.
 50. The array of claim 1, further comprising a depthindicator disposed in at least one buoyant section.
 51. The array ofclaim 1, wherein the buoyant sections comprise hollow microspheres, andwherein a concentration of the hollow microspheres in the buoyantsections is adjusted such that buoyancy of the array is controlled bythe concentration of the hollow microspheres along the length of thestrain member during use.
 52. The array of claim 1, wherein the buoyantsections comprise hollow microspheres, and wherein a density of thehollow microspheres in the buoyant sections is adjusted such thatbuoyancy of the array is controlled by the density of the hollowmicrospheres along the length of the strain member during use.
 53. Thearray of claim 1, wherein buoyancy of the array is substantially uniformalong the length of the strain member during use.
 54. The array of claim1, wherein the buoyant sections comprise hollow microspheres, andwherein a concentration of the hollow microspheres is substantiallyincreased adjacent to a heavier section of the array such that theincreased concentration of the hollow microspheres provides foradditional buoyancy adjacent to the heavier section during use.
 55. Thearray of claim 1, further comprising coupling at least the one sensor toat least one additional sensor to form an active section in the array.56. The array of claim 55, further comprising coupling the activesection to the strain member.
 57. The array of claim 55, furthercomprising coupling the active section to an amplifier.
 58. The array ofclaim 1, further comprising coupling at least the one sensor to at leastone additional sensor in series to form an active section in the array.59. The array of claim 1, further comprising coupling at least the onesensor to at least one additional sensor in parallel to form an activesection in the array.
 60. The array of claim 1, wherein the arraycomprises a towed array.
 61. The array of claim 1, wherein the array isneutrally buoyant in fresh water.
 62. A method for constructing anacoustic sensor array, comprising: encapsulating at least one sensor ina molding material to form at least one sensor section; mounting atleast the one sensor section on a length of a strain member; andencapsulating at least one portion of the strain member in a buoyantmolding material to form at least one buoyant section adjacent to atleast the one sensor section.
 63. The method of claim 62, wherein themolding material comprises hollow micro spheres.
 64. The method of claim62, wherein the molding material comprises polyurethane.
 65. The methodof claim 62, wherein encapsulating at least the one sensor in themolding material comprises using a molding machine.
 66. The method ofclaim 62, wherein encapsulating at least the one sensor in the moldingmaterial comprises using a reaction injection molding process.
 67. Themethod of claim 66, further comprising rotating a molding machine about90° during the reaction injection molding process.
 68. The method ofclaim 62, further comprising temporarily supporting at least the onesensor on a mandrel, wherein the mandrel is removed followingencapsulating of at least the one sensor in the molding material. 69.The method of claim 68, further comprising disposing an o-ring on themandrel such that molding material is inhibited from entering apassageway of at least the one sensor.
 70. The method of claim 68,further comprising helically winding a wire attached to at least the onesensor around a length of the mandrel such that the molding materialencloses the wire in a helical pattern.
 71. The method of claim 68,further comprising threading a wire through a wiring passage in themandrel such that the wire extends outside at least the one sensorsection.
 72. The method of claim 71, further comprising disposing ano-ring on the wire to substantially inhibit expulsion of the moldingmaterial through the wiring passage in the mandrel.
 73. The method ofclaim 68, further comprising mating at least one sleeve to the mandrel.74. The method of claim 73, further comprising inserting a folia againstan inside surface of the at least one sleeve, wherein the folia promotesbonding between the molding material and the buoyant molding material.75. The method of claim 62, further comprising coupling a wire attachedto at least the one sensor to at least one additional sensor.
 76. Themethod of claim 62, further comprising connecting a wire attached to atleast the one sensor to at least one additional electrical device. 77.The method of claim 76, wherein at least the one additional electricaldevice comprises an amplifier.
 78. The method of claim 76, wherein atleast the one additional electrical device comprises a telemetry module.79. The method of claim 76, wherein at least the one additionalelectrical device comprises a depth indicator.
 80. The method of claim76, wherein at least the one additional electrical device comprises anaccelerometer.
 81. The method of claim 62, further comprising disposinga potting material between at least the one sensor section and thestrain member.
 82. The method of claim 81, wherein the potting materialbonds at least the one sensor section to the strain member.
 83. Themethod of claim 81, wherein the potting material comprises polyurethane.84. The method of claim 62, wherein encapsulating at least the oneportion of the strain member adjacent to at least the one sensor sectionin the buoyant molding material comprises using a molding machine. 85.The method of claim 62, wherein encapsulating at least the one portionof the strain member adjacent to at least the one sensor section in thebuoyant molding material comprises using a reaction injection moldingprocess.
 86. The method of claim 85, further comprising rotating amolding machine about 90° during the reaction injection molding process.87. The method of claim 62, wherein the buoyant molding materialcomprises hollow micro spheres.
 88. The method of claim 62, wherein thebuoyant molding material comprises polyurethane.
 89. The method of claim62, further comprising substantially bonding the buoyant moldingmaterial to the molding material.
 90. The method of claim 62, furthercomprising substantially bonding the buoyant molding material to themolding material such that fluid is inhibited from entering the array.91. The method of claim 62, wherein the buoyant molding materialcomprises hollow microspheres, the method further comprising adjusting aconcentration of the hollow microspheres in the buoyant molding materialsuch that buoyancy of the array is controlled by the concentration ofthe hollow microspheres.
 92. The method of claim 91, further comprisingadjusting the concentration of the hollow microspheres such thatbuoyancy of the array is substantially uniform along its length.
 93. Themethod of claim 91, further comprising increasing the concentration ofthe hollow microspheres adjacent to a heavier section of the array suchthat the increased concentration provides additional buoyancy adjacentto the heavier section.
 94. The method of claim 62, further comprisingencapsulating more than one sensor in the molding material to form atleast the one sensor section.
 95. The method of claim 62, wherein atleast the one sensor comprises a hydrophone.
 96. The method of claim 62,wherein at least the one sensor comprises a molded base, the methodfurther comprising disposing the molded base in a diaphragm.
 97. Themethod of claim 96, wherein the diaphragm comprises one or more concavesurfaces.
 98. The method of claim 96, wherein the diaphragm comprises atubular member.
 99. The method of claim 96, further comprising formingat least one air gap between the molded base and the diaphragm.
 100. Themethod of claim 96, wherein at least the one sensor comprises apiezoelectric film.
 101. The method of claim 100, further comprisingsurrounding a portion of the diaphragm with the piezoelectric film. 102.The method of claim 100, further comprising fastening the piezoelectricfilm to the diaphragm.
 103. The method of claim 100, wherein thepiezoelectric film comprises polyvinylidiene.
 104. The method of claim100, wherein the piezoelectric film comprises a conductive pattern on aface of the film.
 105. The method of claim 104, wherein the conductivepattern comprises at least one conductive area and at least onenon-conductive strip, wherein at least the one conductive area ispositioned above a concave surface of the molded base, and wherein atleast the one non-conductive strip is positioned above a ridge of themolded base.
 106. The method of claim 104, wherein the conductivepattern comprises at least one conductive area, and wherein at least theone conductive area couples to at least one pin disposed on an edge ofthe piezoelectric film.
 107. The method of claim 106, further comprisingcoupling at least the one pin to at least one wire.
 108. The method ofclaim 104, further comprising disposing at least the one sensor within ashield.
 109. The method of claim 108, wherein the shield comprises ametal layer disposed on the polyester base material.
 110. The method ofclaim 104, wherein at least the one sensor comprises a piezoelectricfilm, wherein the shield has a substantially similar size and shape asthe piezoelectric film, and wherein the shield substantially surrounds aportion of the piezoelectric film.
 111. The method of claim 62, furthercomprising disposing a cup around at least the one sensor.
 112. Themethod of claim 111, wherein the cup comprises longitudinal fibersdisposed in an adhesive matrix.
 113. The method of claim 112, furthercomprising forming the cup by pulltruding the longitudinal fibers intothe adhesive matrix.
 114. The method of claim 111, further comprisingdisposing a filling material between the cup and at least the onesensor.
 115. The method of claim 114, wherein the filling materialcomprises A-00 polyurethane.
 116. The method of claim 111, furthercomprising sealing the filling material within the cup.
 117. The methodof claim 111, wherein the filling material is configured to reducecoupling between at least the one sensor and shear energies present at aflow boundary on the array.
 118. The method of claim 62, wherein atleast the one sensor comprises a fiber optic sensor.
 119. The method ofclaim 62, further comprising coupling an end connector to the strainmember.
 120. The method of claim 119, wherein the end connector isencapsulated in the buoyant molding material.
 121. The method of claim62, wherein at least the one buoyant section has an outer diametersubstantially similar to an outer diameter of at least the one sensorsection.
 122. The method of claim 62, wherein the array comprises atowed array.
 123. A method for constructing an acoustic sensor array,comprising: mounting at least one sensor on a length of a strain member;moving the strain member so that at least the one sensor is positionedin a first molding press; encapsulating at least the one sensor in amolding material to form at least one sensor section; moving the strainmember so that a portion of the strain member is positioned in a secondmolding press; and encapsulating the portion of the strain member in abuoyant molding material to form at least one buoyant section on thestrain member, wherein the portion is adjacent to at least the onesensor section.
 124. The method of claim 123, wherein moving the strainmember comprises using a reel.
 125. The method of claim 124, furthercomprising electrically operating the reel.
 126. The method of claim124, further comprising using an additional reel to apply tension to thestrain member.
 127. The method of claim 123, wherein mounting at leastthe one sensor comprises disposing a potting material between at leastthe one sensor and the strain member.
 128. The method of claim 123,wherein the molding material comprises hollow microspheres.
 129. Themethod of claim 123, wherein the molding material comprisespolyurethane.
 130. The method of claim 123, wherein encapsulating atleast the one sensor in the molding material comprises using a reactioninjection molding process.
 131. The method of claim 123, whereinencapsulating at least the one portion of the strain member adjacent toat least the one sensor section in the buoyant molding materialcomprises using a reaction injection molding process.
 132. The method ofclaim 123, wherein the buoyant molding material comprises hollowmicrospheres.
 133. The method of claim 123, wherein the buoyant moldingmaterial comprises polyurethane.
 134. The method of claim 123, furthercomprising encapsulating more than one sensor in the molding material toform at least the one sensor section.
 135. The method of claim 123,wherein at least the one sensor comprises a hydrophone.
 136. The methodof claim 123, further comprising coupling an end connector to the strainmember.
 137. The method of claim 123, wherein the array comprises atowed array.
 138. An acoustic sensor array, comprising: a strain memberhaving a length; sensor sections positioned along the length of themember, wherein at least one sensor is disposed within each sensorsection; buoyant sections positioned between the sensor sections,wherein the buoyant sections comprise hollow microspheres; and whereinthe strain member, the sensor sections, and the buoyant sections arejoined to form the array.
 139. The array of claim 138, wherein at leastthe one sensor comprises a hydrophone.
 140. The array of claim 138,further comprising a cup disposed around at least the one sensor. 141.The array of claim 140, wherein the cup comprises longitudinal fibersdisposed in an adhesive matrix.
 142. The array of claim 140, furthercomprising a filling material disposed between the cup and at least theone sensor.
 143. The array of claim 142, wherein the filling materialcomprises A-00 polyurethane.
 144. The array of claim 138, wherein atleast the one sensor comprises a fiber optic sensor.
 145. The array ofclaim 138, further comprising a potting material disposed between eachsensor section and the strain member.
 146. The array of claim 145,wherein the potting material substantially bonds to each sensor sectionand the strain member.
 147. The array of claim 138, wherein the strainmember, the sensor sections, and the buoyant sections are molded to formthe array.
 148. The array of claim 138, wherein the sensor sectionscomprise a reaction injection molded material.
 149. The array of claim138, wherein the sensor sections comprise a hollow microsphere moldingmaterial.
 150. The array of claim 138, wherein the sensor sectionscomprise a polyurethane material.
 151. The array of claim 138, whereinthe buoyant sections comprise a reaction injection molded material. 152.The array of claim 138, wherein the buoyant sections comprise apolyurethane material.
 153. The array of claim 138, wherein each buoyantsection is substantially bonded to at least one sensor section and thestrain member such that fluid is inhibited from entering the arrayduring use.
 154. The array of claim 138, wherein the buoyant sectionshave an outer diameter substantially similar to an outer diameter of thesensor sections.
 155. The array of claim 138, wherein the array has asubstantially constant outer diameter.
 156. The array of claim 138,wherein a concentration of the hollow microspheres in the buoyantsections is adjusted such that buoyancy of the array is controlled bythe concentration of the hollow microspheres along the length of thestrain member during use.
 157. The array of claim 138, wherein a densityof the hollow microspheres in the buoyant sections is adjusted such thatbuoyancy of the array is controlled by the density of the hollowmicrospheres along the length of the strain member during use.
 158. Thearray of claim 138, wherein buoyancy of the array is substantiallyuniform along the length of the strain member during use.
 159. The arrayof claim 138, wherein a concentration of the hollow microspheres issubstantially increased adjacent to a heavier section of the array suchthat the increased concentration of the hollow microspheres provides foradditional buoyancy adjacent to the heavier section during use.
 160. Thearray of claim 138, wherein the array comprises a towed array.
 161. Thearray of claim 138, wherein the array is neutrally buoyant in freshwater.
 162. A method for constructing an acoustic sensor array,comprising: encapsulating at least one sensor in a molding material toform at least one sensor section; mounting at least the one sensorsection on a length of a strain member; and encapsulating at least oneportion of the strain member in a buoyant molding material to form atleast one buoyant section adjacent to at least the one sensor section,wherein the buoyant molding material comprises hollow microspheres. 163.The method of claim 162, wherein the molding material comprises hollowmicrospheres.
 164. The method of claim 162, wherein the molding materialcomprises polyurethane.
 165. The method of claim 162, whereinencapsulating at least the one sensor in the molding material comprisesusing a molding machine.
 166. The method of claim 162, whereinencapsulating at least the one sensor in the molding material comprisesusing a reaction injection molding process.
 167. The method of claim162, further comprising disposing a potting material between at leastthe one sensor section and the strain member.
 168. The method of claim162, wherein encapsulating at least the one portion of the strain memberadjacent to at least the one sensor section in the buoyant moldingmaterial comprises using a molding machine.
 169. The method of claim162, wherein encapsulating at least the one portion of the strain memberadjacent to at least the one sensor section in the buoyant moldingmaterial comprises using a reaction injection molding process.
 170. Themethod of claim 162, wherein the buoyant molding material comprisespolyurethane.
 171. The method of claim 162, further comprisingsubstantially bonding the buoyant molding material to the moldingmaterial.
 172. The method of claim 162, further comprising substantiallybonding the buoyant molding material to the molding material such thatfluid is inhibited from entering the array during use of the array. 173.The method of claim 162, further comprising adjusting a concentration ofthe hollow microspheres in the buoyant molding material such thatbuoyancy of the array is controlled by the concentration of the hollowmicrospheres.
 174. The method of claim 162, further comprisingencapsulating more than one sensor in the molding material to form atleast the one sensor section.
 175. The method of claim 162, wherein atleast the one sensor comprises a hydrophone.
 176. The method of claim162, further comprising disposing a cup around at least the one sensor.177. The method of claim 176, wherein the cup comprises longitudinalfibers disposed in an adhesive matrix.
 178. The method of claim 177,further comprising forming the cup by pulltruding the longitudinalfibers into the adhesive matrix.
 179. The method of claim 176, furthercomprising disposing a filling material between the cup and at least theone sensor.
 180. The method of claim 179, wherein the filling materialcomprises A-00 polyurethane.
 181. The method of claim 162, wherein atleast the one sensor comprises a fiber optic sensor.
 182. The method ofclaim 162, wherein the array comprises a towed array.
 183. An acousticsensor array, comprising: a strain member having a length; sensorsections positioned along the length of the member, wherein more thanone sensor is disposed within each sensor section; buoyant sectionspositioned between the sensor sections; and wherein the strain member,the sensor sections, and the buoyant sections are joined to form thearray.
 184. The array of claim 183, wherein the more than one sensorcomprises a hydrophone.
 185. The array of claim 183, further comprisinga cup disposed around the more than one sensor.
 186. The array of claim185, wherein the cup comprises longitudinal fibers disposed in anadhesive matrix.
 187. The array of claim 185, further comprising afilling material disposed between the cup and the more than one sensor.188. The array of claim 187, wherein the filling material comprises A-00polyurethane.
 189. The array of claim 183, wherein the more than onesensor comprises a fiber optic sensor.
 190. The array of claim 183,further comprising a potting material disposed between each sensorsection and the strain member.
 191. The array of claim 183, wherein thepotting material substantially bonds to each sensor section and thestrain member.
 192. The array of claim 183, wherein the strain member,the sensor sections, and the buoyant sections are molded to form thearray.
 193. The array of claim 183, wherein the sensor sections comprisea reaction injection molded material.
 194. The array of claim 183,wherein the sensor sections comprise a hollow microsphere moldingmaterial.
 195. The array of claim 183, wherein the sensor sectionscomprise a polyurethane material.
 196. The array of claim 183, whereinthe buoyant sections comprise a reaction injection molded material. 197.The array of claim 183, wherein the buoyant sections comprise hollowmicrospheres.
 198. The array of claim 183, wherein the buoyant sectionscomprise a polyurethane material.
 199. The array of claim 183, whereineach buoyant section is substantially bonded to at least one sensorsection and the strain member such that fluid is inhibited from enteringthe array during use.
 200. The array of claim 183, wherein the buoyantsections have an outer diameter substantially similar to an outerdiameter of the sensor sections.
 201. The array of claim 183, whereinthe array has a substantially constant outer diameter.
 202. The array ofclaim 183, wherein the buoyant sections comprise hollow microspheres,and wherein a concentration of the hollow microspheres in the buoyantsections is adjusted such that buoyancy of the array is controlled bythe concentration of the hollow microspheres along the length of thestrain member during use.
 203. The array of claim 183, wherein thebuoyant sections comprise hollow microspheres, and wherein a density ofthe hollow microspheres in the buoyant sections is adjusted such thatbuoyancy of the array is controlled by the density of the hollowmicrospheres along the length of the strain member during use.
 204. Thearray of claim 183, wherein buoyancy of the array is substantiallyuniform along the length of the strain member during use.
 205. The arrayof claim 183, wherein the buoyant sections comprise hollow microspheres,and wherein a concentration of the hollow microspheres is substantiallyincreased adjacent to a heavier section of the array such that theincreased concentration of the hollow microspheres provides foradditional buoyancy adjacent to the heavier section during use.
 206. Thearray of claim 183, wherein the array comprises a towed array.
 207. Thearray of claim 183, wherein the array is neutrally buoyant in freshwater.
 208. A method for constructing an acoustic sensor array,comprising: encapsulating more than one sensor in a molding material toform at least one sensor section; mounting at least the one sensorsection on a length of a strain member; and encapsulating at least oneportion of the strain member in a buoyant molding material to form atleast one buoyant section adjacent to at least the one sensor section.209. The method of claim 208, wherein the molding material compriseshollow microspheres.
 210. The method of claim 208, wherein the moldingmaterial comprises polyurethane.
 211. The method of claim 208, whereinencapsulating the more than one sensor in the molding material comprisesusing a molding machine.
 212. The method of claim 208, whereinencapsulating the more than one sensor in the molding material comprisesusing a reaction injection molding process.
 213. The method of claim208, further comprising disposing a potting material between at leastthe one sensor section and the strain member.
 214. The method of claim208, wherein encapsulating at least the one portion of the strain memberadjacent to at least the one sensor section in the buoyant moldingmaterial comprises using a molding machine.
 215. The method of claim208, wherein encapsulating at least the one portion of the strain memberadjacent to at least the one sensor section in the buoyant moldingmaterial comprises using a reaction injection molding process.
 216. Themethod of claim 208, wherein the buoyant molding material comprisespolyurethane.
 217. The method of claim 208, wherein the buoyant moldingmaterial comprises hollow microspheres.
 218. The method of claim 208,further comprising substantially bonding the buoyant molding material tothe molding material.
 219. The method of claim 208, further comprisingsubstantially bonding the buoyant molding material to the moldingmaterial such that fluid is inhibited from entering the array during useof the array.
 220. The method of claim 208, wherein the buoyant moldingmaterial comprises hollow microspheres, the method further comprisingadjusting a concentration of the hollow microspheres in the buoyantmolding material such that buoyancy of the array is controlled by theconcentration of the hollow microspheres.
 221. The method of claim 208,wherein the more than one sensor comprises a hydrophone.
 222. The methodof claim 208, further comprising disposing a cup around the more thanone sensor.
 223. The method of claim 222, wherein the cup compriseslongitudinal fibers disposed in an adhesive matrix.
 224. The method ofclaim 223, further comprising forming the cup by pulltruding thelongitudinal fibers into the adhesive matrix.
 225. The method of claim222, further comprising disposing a filling material between the cup andthe more than one sensor.
 226. The method of claim 225, wherein thefilling material comprises A-00 polyurethane.
 227. The method of claim208, wherein the more than one sensor comprises a fiber optic sensor.228. The method of claim 208, wherein the array comprises a towed array.229. An acoustic sensor array, comprising: a strain member having alength; sensor sections positioned along the length of the member,wherein at least one sensor is disposed within each sensor section,wherein at least the one sensor is disposed in a cup, and wherein thecup is configured to inhibit deformation of at least the one sensor in alongitudinal direction during use; a filling material disposed betweenthe cup and at least the one sensor; buoyant sections positioned betweenthe sensor sections; and wherein the strain member, the sensor sections,and the buoyant sections are joined to form the array.
 230. The array ofclaim 229, wherein at least the one sensor comprises a hydrophone. 231.The array of claim 229, wherein the cup comprises longitudinal fibersdisposed in an adhesive matrix.
 232. The array of claim 229, wherein thefilling material comprises A-00 polyurethane.
 233. The array of claim229, wherein at least the one sensor comprises a fiber optic sensor.234. The array of claim 229, further comprising a potting materialdisposed between each sensor section and the strain member.
 235. Thearray of claim 229, wherein the strain member, the sensor sections, andthe buoyant sections are molded to form the array.
 236. The array ofclaim 229, wherein the sensor sections comprise a reaction injectionmolded material.
 237. The array of claim 229, wherein the sensorsections comprise a hollow microsphere molding material.
 238. The arrayof claim 229, wherein the sensor sections comprise a polyurethanematerial.
 239. The array of claim 229, wherein the buoyant sectionscomprise a reaction injection molded material.
 240. The array of claim229, wherein the buoyant sections comprise hollow micro spheres. 241.The array of claim 229, wherein the buoyant sections comprise apolyurethane material.
 242. The array of claim 229, wherein each buoyantsection is substantially bonded to at least one sensor section and thestrain member such that fluid is inhibited from entering the arrayduring use.
 243. The array of claim 229, wherein the buoyant sectionshave an outer diameter substantially similar to an outer diameter of thesensor sections.
 244. The array of claim 229, wherein the array has asubstantially constant outer diameter.
 245. The array of claim 229,wherein the buoyant sections comprise hollow microspheres, and wherein aconcentration of the hollow microspheres in the buoyant sections isadjusted such that buoyancy of the array is controlled by theconcentration of the hollow microspheres along the length of the strainmember during use.
 246. The array of claim 229, wherein the buoyantsections comprise hollow microspheres, and wherein a density of thehollow microspheres in the buoyant sections is adjusted such thatbuoyancy of the array is controlled by the density of the hollowmicrospheres along the length of the strain member during use.
 247. Thearray of claim 229, wherein buoyancy of the array is substantiallyuniform along the length of the strain member during use.
 248. The arrayof claim 229, wherein the buoyant sections comprise hollow microspheres,and wherein a concentration of the hollow microspheres is substantiallyincreased adjacent to a heavier section of the array such that theincreased concentration of the hollow microspheres provides foradditional buoyancy adjacent to the heavier section during use.
 249. Thearray of claim 229, wherein the array comprises a towed array.
 250. Amethod for constructing an acoustic sensor array, comprising: disposingat least one sensor in a cup, wherein the cup is configured to inhibitdeformation of at least the one sensor in a longitudinal directionduring use; filling a space between at least the one sensor and the cupwith a filling material; encapsulating at least the one sensor in amolding material to form at least one sensor section; mounting at leastthe one sensor section on a length of a strain member; and encapsulatingat least one portion of the strain member in a buoyant molding materialto form at least one buoyant section adjacent to at least the one sensorsection.
 251. The method of claim 250, wherein the molding materialcomprises hollow micro spheres.
 252. The method of claim 250, whereinthe molding material comprises polyurethane.
 253. The method of claim250, wherein encapsulating at least the one sensor in the moldingmaterial comprises using a molding machine.
 254. The method of claim250, wherein encapsulating at least the one sensor in the moldingmaterial comprises using a reaction injection molding process.
 255. Themethod of claim 250, further comprising disposing a potting materialbetween at least the one sensor section and the strain member.
 256. Themethod of claim 250, wherein encapsulating at least the one portion ofthe strain member adjacent to at least the one sensor section in thebuoyant molding material comprises using a molding machine.
 257. Themethod of claim 250, wherein encapsulating at least the one portion ofthe strain member adjacent to at least the one sensor section in thebuoyant molding material comprises using a reaction injection moldingprocess.
 258. The method of claim 250, wherein the buoyant moldingmaterial comprises polyurethane.
 259. The method of claim 250, whereinthe buoyant molding material comprises hollow microspheres.
 260. Themethod of claim 250, further comprising substantially bonding thebuoyant molding material to the molding material.
 261. The method ofclaim 250, further comprising substantially bonding the buoyant moldingmaterial to the molding material such that fluid is inhibited fromentering the array during use of the array.
 262. The method of claim250, wherein the buoyant molding material comprises hollow microspheres,the method further comprising adjusting a concentration of the hollowmicrospheres in the buoyant molding material such that buoyancy of thearray is controlled by the concentration of the hollow microspheres.263. The method of claim 250, further comprising encapsulating more thanone sensor in the molding material to form at least the one sensorsection.
 264. The method of claim 250, wherein at least the one sensorcomprises a hydrophone.
 265. The method of claim 250, wherein the cupcomprises longitudinal fibers disposed in an adhesive matrix.
 266. Themethod of claim 265, further comprising forming the cup by pulltrudingthe longitudinal fibers into the adhesive matrix.
 267. The method ofclaim 250, wherein the filling material comprises A-00 polyurethane.268. The method of claim 250, wherein at least the one sensor comprisesa fiber optic sensor.
 269. The method of claim 250, wherein the arraycomprises a towed array.
 270. An acoustic sensor array, comprising: astrain member having a length; sensor sections positioned along thelength of the member, wherein at least one fiber optic sensor isdisposed within each sensor section; buoyant sections positioned betweenthe sensor sections; and wherein the strain member, the sensor sections,and the buoyant sections are joined to form the array.
 271. The array ofclaim 270, wherein the strain member comprises an aramide stress member.272. The array of claim 270, further comprising a potting materialdisposed between each sensor section and the strain member.
 273. Thearray of claim 270, wherein the strain member, the sensor sections, andthe buoyant sections are molded to form the array.
 274. The array ofclaim 270, wherein the sensor sections comprise a reaction injectionmolded material.
 275. The array of claim 270, wherein the sensorsections comprise a hollow microsphere molding material.
 276. The arrayof claim 270, wherein the sensor sections comprise a polyurethanematerial.
 277. The array of claim 270, wherein the buoyant sectionscomprise a reaction injection molded material.
 278. The array of claim270, wherein the buoyant sections comprise hollow micro spheres. 279.The array of claim 270, wherein the buoyant sections comprise apolyurethane material.
 280. The array of claim 270, wherein each buoyantsection is substantially bonded to at least one sensor section and thestrain member such that fluid is inhibited from entering the arrayduring use.
 281. The array of claim 270, wherein the buoyant sectionshave an outer diameter substantially similar to an outer diameter of thesensor sections.
 282. The array of claim 270, wherein the array has asubstantially constant outer diameter.
 283. The array of claim 270,wherein the buoyant sections comprise hollow microspheres, and wherein aconcentration of the hollow microspheres in the buoyant sections isadjusted such that buoyancy of the array is controlled by theconcentration of the hollow microspheres along the length of the strainmember during use.
 284. The array of claim 270, wherein the buoyantsections comprise hollow microspheres, and wherein a density of thehollow microspheres in the buoyant sections is adjusted such thatbuoyancy of the array is controlled by the density of the hollowmicrospheres along the length of the strain member during use.
 285. Thearray of claim 270, wherein buoyancy of the array is substantiallyuniform along the length of the strain member during use.
 286. The arrayof claim 270, wherein the buoyant sections comprise hollow microspheres,and wherein a concentration of the hollow microspheres is substantiallyincreased adjacent to a heavier section of the array such that theincreased concentration of the hollow microspheres provides foradditional buoyancy adjacent to the heavier section during use.
 287. Thearray of claim 270, wherein the array comprises a towed array.
 288. Amethod for constructing an acoustic sensor array, comprising:encapsulating at least one fiber optic sensor in a molding material toform at least one sensor section; mounting at least the one sensorsection on a length of a strain member; and encapsulating at least oneportion of the strain member in a buoyant molding material to form atleast one buoyant section adjacent to at least the one sensor section.289. The method of claim 288, wherein the molding material compriseshollow microspheres.
 290. The method of claim 288, wherein the moldingmaterial comprises polyurethane.
 291. The method of claim 288, whereinencapsulating at least the one fiber optic sensor in the moldingmaterial comprises using a molding machine.
 292. The method of claim288, wherein encapsulating at least the one fiber optic sensor in themolding material comprises using a reaction injection molding process.293. The method of claim 288, further comprising disposing a pottingmaterial between at least the one sensor section and the strain member.294. The method of claim 288, wherein encapsulating at least the oneportion of the strain member adjacent to at least the one sensor sectionin the buoyant molding material comprises using a molding machine. 295.The method of claim 288, wherein encapsulating at least the one portionof the strain member adjacent to at least the one sensor section in thebuoyant molding material comprises using a reaction injection moldingprocess.
 296. The method of claim 288, wherein the buoyant moldingmaterial comprises polyurethane.
 297. The method of claim 288, whereinthe buoyant molding material comprises hollow microspheres.
 298. Themethod of claim 288, further comprising substantially bonding thebuoyant molding material to the molding material.
 299. The method ofclaim 288, further comprising substantially bonding the buoyant moldingmaterial to the molding material such that fluid is inhibited fromentering the array during use of the array.
 300. The method of claim288, wherein the buoyant molding material comprises hollow microspheres,the method further comprising adjusting a concentration of the hollowmicrospheres in the buoyant molding material such that buoyancy of thearray is controlled by the concentration of the hollow microspheres.301. The method of claim 288, further comprising encapsulating more thanone sensor in the molding material to form at least the one sensorsection.
 302. The method of claim 288, wherein the array comprises atowed array.